In voice communications networks, such as voice over IP networks, transcoding refers to converting from one type of voice compression to another. Transcoding is necessary when different legs of a call have incompatible coder/decoders (codecs); however, when the different legs of a call use compatible codecs, it is desirable to establish a transcoding free connection. Establishing a transcoding free connection is desirable because transcoding introduces delay and degrades voice quality. The terms “transcoder free” and “transcoding free” are used interchangeably herein to refer to the absence of transcoding in a connection.
It may be desirable to establish a transcoder free connection when both legs of a call are UMTS. It may also be desirable to establish a transcoder free connection when at least one leg of a call is not UMTS. For example, it may be desirable to establish a transcoder free connection between a UMA call leg and a UMTS call leg. Third Generation Partnership Project (3GPP) Technical Standard TS 29.163 requires transcoder free operation when an IP multimedia media gateway (IM-MGW) is used to bridge a connection between an Nb and an Mb interface. An Mb interface is an interface between the media gateway and an access point in the UMA network. An Nb interface is an interface between the media gateway and another media gateway in the UMTS network.
Although the above-referenced 3GPP standard indicates that transcoder free operation should be implemented by an IM-MGW, the technical standard fails to describe any hardware or software necessary to achieve such operation. Moreover, the technical standard omits many of the details required for transcoder free operation. For example, the technical standard fails to address timing issues with regard to rate control, redundancy reconciliation between the UMA and UMTS networks, and differences in packetization timing between the UMA and UMTS networks.
Accordingly, in light of these difficulties, there exists a need for methods, systems, and computer program products for providing transcoder free operation and interworking between UMA and UMTS call legs using a media gateway.